Celestial bronze weapons will not harm mortals, as they are 'not important enough' to be harmed by them. Celestial bronze is forged in the heart of Mount Etna and cooled in the River Lethe. Demigods and gods favor celestial bronze weapons because they are able to wound immortals, monsters, and creatures of the underworld, but cannot harm mortals- it will pass through them like an illusion, whereas mundane iron or steel weapons bounce off of most magical beings uselessly. Demigods, being half god and half mortal, can be affected by either celestial or normal weapons. Celestial bronze is also used in god armor and most likely demigod armor.
Chemical Symbol: CuSn* (* means its a magically Alloy)